


Resonant Frequency

by magumarashi



Series: GBF Headcanons [11]
Category: Granblue Fantasy (Video Game)
Genre: F/M, Femdom, Vibrators, butt stuff, whiny bottom sandalphon
Language: English
Status: Completed
Published: 2019-09-06
Updated: 2019-09-06
Packaged: 2020-10-11 00:54:58
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,192
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20537495
Author URL: https://archiveofourown.org/users/magumarashi/pseuds/magumarashi
Summary: Rather than beating hearts, Primal Beasts have humming cores to facilitate the movement of energy within their bodies. When two things vibrate in tandem, some kind of reaction is only a matter of course...





	Resonant Frequency

**Author's Note:**

> so uhhhhh i must have gotten this idea in like. december? january? it was months ago, like embarrassingly long, and i've been chipping away at this little by little. but since writing porn requires me to be a) horny and b) not at work, you can imagine the opportunities to work on this were few and far between
> 
> anyway i'm really glad to finally have this done, enjoy ya nasties
> 
> i should probably add that this is post-000 lmao (and probably contiguous with my other sandjeeta fics). Djeeta has been aged up to her early twenties.

It took Djeeta a few months to notice it; the ambient sounds of the Grandcypher usually drowned out any other subtle noises. It was only when she and Sandalphon were traversing a misty mountain field for a quest that she finally noticed a faint, low humming coming from his body.

“Is that sound… coming from you?” she asked.

He looked at her quizzically for a moment before responding, “Oh, you mean my core?”

“Your…?”

“Right, of course you wouldn’t know,” Sandalphon sighed to himself. “Primals don’t have beating hearts like skydwellers do. Instead, our cores facilitate the movement of energy within our bodies. They vibrate slightly as they do this, hence the sound. It’s usually so quiet as to be inaudible, though… You would have to physically put your ear to me to hear it.”

“Huh…” said Djeeta. None of the other Primals in her crew had ever mentioned anything like this; until now she had assumed they had hearts like everyone else.

“It’s so quiet here… I suppose I hadn’t noticed that my core might be audible to others,” Sandalphon reflected. “Is it bothering you?”

“Oh, not at all!” said Djeeta. “I’ve spent so long on airships that I’m used to a little ambient noise.”

Sandalphon smirked.

“Good. Let’s continue on, then. We must be getting close now.”

“Yeah!”

* * *

In the months that followed, Djeeta would become more familiar with the primarch’s core. Sandalphon showed her where it was: unlike skydweller hearts, his core was directly in the center of his chest, and set back a little; its warmth could be most easily felt at the joint where his six wings met his back. She could hear it each time she lay her head on his chest, as though putting her ear to the Grandcypher’s walls to feel the distant rumble of the engines. _His_ sound, though, was a gentle, steady hum—oddly organic, unfamiliar. Strange to hear in place of a heartbeat, and yet somehow calming. On lazy mornings when the two of them had little other to do than lie in bed together, tangled in each other’s arms, she could hear his core humming with excitement. Sometimes she could even physically feel the vibration against her chest.

It took a bit longer to discover that cores had yet another property—this one unknown to even the Primals themselves.

It had started, oddly enough, with a box of bedroom toys. (Djeeta had received them as a gift from Metera, along with a fellow bachelorette’s wink and nod.) Sandalphon seemed open to the suggestion that they try one together, and they spent a few minutes going over the various items. The primarch looked at most of them with a mixture of concern and mistrust, which Djeeta supposed was understandable. Their intended usage wasn’t always immediately apparent from their shape, and not all of them had unisex designs. Finally, Sandalphon settled on a small, thin one with a flared base. A cord ran from the base to a small controller with a knob.

“This one looks easiest to use.”

“Yeah, that’s a fair bet,” said Djeeta. She’d never used that one herself, but she could tell immediately what it did—the cord was a giveaway. She wondered if he’d let her turn it on…

“How _is_ this one used?” Sandalphon asked.

“It goes, uh…” Djeeta smiled awkwardly. “Up your butt. Or mine, if you’d rather.”

“… Interesting,” Sandalphon replied, though from his tone of voice it seemed his curiosity was piqued. “Would you do the honors then, _captain?”_

Djeeta could only stare at him, at first—_He’s already ready to try it!?_

“Er, I’d be happy to,” she answered finally, smiling. “I’m surprised you’re already so into this idea, though… lots of skydwellers are at least a little nervous about putting stuff up their butts.”

“To be honest, I don’t actually know if I’ll feel anything,” Sandalphon admitted. “Primals’ bodies were modeled fairly closely after those of skydwellers and Astrals, but…”

“Right,” said Djeeta. “This seems like an awfully specific detail to include…”

“However, if I’ve learned anything in our time together, it’s that the Astrals spared no detail in our designs—even the most salacious,” Sandalphon added with a wry smirk. “So I think it would be worth a try nonetheless.”

“Alright then,” said Djeeta, motioning to him with her fingers. “Turn around for me, will you?”

Sandalphon was quick to obey; he shuffled around on the covers so that he was facing away from her. They’d abandoned their clothing a while ago, and Djeeta took a minute to admire the primarch’s lithe body—the angles of his back, the curves of his perfect legs… They’d been together for some time now, but part of her still couldn’t believe that this beautiful sight was hers whenever she wanted it.

“Enjoying the view?” Sandalphon teased over his shoulder.

“Mm-hm,” said Djeeta. “Alright, now just relax…”

She reached forward and gently began to massage him at the rim. At first he jumped at her touch, but before long he slowly began to melt at her fingertips. He let out a weak sigh, leaning into her movements slightly.

“Ohh, that’s….” he said, “That’s more sensitive than I thought…”

“Mm. You like that?”

“It’s… not half bad…”

“Alright. I’m going to try putting it in now, then.”

“Go… go ahead…!”

After making sure he’d loosened up a bit, Djeeta squirted a bit of lube onto the toy and gently pushed it inside—eliciting a gasp from her partner. Once she was certain that it was snug, she sat back a little bit to admire her handiwork. The vibrator’s flared base kept it from vanishing out of sight; from her vantage point she could see it nestled between his cheeks.

“How’s it feel?” she asked gently.

“R-really good…” Sandalphon’s voice shook—with pleasure or embarrassment, Djeeta couldn’t be sure. Perhaps both. “I didn’t expect it to feel this good….”

“Good!” said Djeeta. She tapped on it a little, and Sandalphon let out a whimper. “Oh? Did you like that?”

Sandalphon nodded into the pillow, so Djeeta took the base between her fingers and wiggled it around a little bit.

“Ah—!”

His startled gasps were enough; she had him metaphorically and literally between her fingers now. It was a nice change of pace: usually she preferred to be the one on the receiving end of sexual exchanges, but she had to admit that taking charge for once wasn’t so bad.

“Can I turn it on?” she asked.

“It—it turns on?!”

Djeeta snorted.

“What did you think the cord was for?”

“To pull it out, what else!!”

“Oh, you sweet summer child.” Djeeta couldn’t help giggling.

“What, er… what does it do when you turn it on?” Sandalphon asked.

“It vibrates.”

“It—!?”

Figuring it would be easier to show than tell, Djeeta turned the knob on the controller to the first notch. The vibrator began to buzz with a low hum, and Sandalphon nearly jumped out of his skin.

“Ah—?!”

“Like that,” said Djeeta, turning it off again. “How was tha—?!”

_“Turn it back on.”_

For a second or two there was silence—he’d spoken so quickly that it took Djeeta that long to parse what he’d said.

“You want me to turn it back on?”

“D-did I stutter?” said Sandalphon, definitely stuttering.

“That good, huh?” said Djeeta, smirking. She waved the controller a little, coyly. “Maybe I’ll turn it back on if you say please.”

Sandalphon turned to look at her over his shoulder, glowering.

“Turn it back on…. Please.”

“Good boy.”

Djeeta turned the knob back up, and Sandalphon gasped before burying his face back into the pillow to muffle his voice. She’d never _seen_ a man melt so fast; in seconds the Supreme Primarch had been reduced to a quivering, whimpering ball.

_Is this really the lowest setting? _Djeeta found herself wondering.

“Having a good time?” she asked.

“M-my core…!” He responded as best he could between needy gasps. “It’s—my core—!”

“What do you mean, your core?” Djeeta asked, dropping her previous coyness in an instant. She stopped the vibrator again, and the archangel let out a disappointed whine. “Am I hurting you—?!”

“No… far from it,” he said. “The vibration from that… that _thing… _it’s resonating with my core.”

“Huh…” said Djeeta. She supposed it made sense—two things vibrating in tandem were bound to interact with each other somehow. “So… bad? Good?”

“The feeling is…” Sandalphon bit his lip in embarrassment. “… very, _very_ pleasurable.”

“I _see,”_ said Djeeta. “So you probably want me to leave this on until you come, huh?”

“If…. If you’re willing to….”

“Hmm…” Djeeta put her finger back on the knob. Though she didn’t want to give it to him that easily, she had a few ideas in mind already. “Let’s see…”

She turned it up a little bit, higher than the first time; Sandalphon let out a yelp as his whole body shook in response.

“This is still pretty low on the dial,” she said languidly. “It’s at 2 now—do you want to know how high it goes?”

Sandalpon could only nod back to her.

_“Ten,”_ said Djeeta, grinning. “Let’s work our way up, shall we? It’s still early, and I could watch you do this all night.”

_“Djeeta…!” _Sandalphon’s voice came from deep in his throat this time.

“Ooh, that was a good sound,” said Djeeta. “How’s this for a little game? I’ll only turn it up if you _beg_ me to.”

Sandalphon let out a groan; half excited at the prospect of more, yet half disappointed that he would have to work for it.

“I’ll wait,” said Djeeta. She turned the vibrator off again for good measure, reminding him who was in control.

_“Ugh…”_ Sandalphon groaned. “How long… do you intend to keep me waiting…?”

“Mm, that depends on you,” she said, though she supposed his question counted as begging of a sort. She turned the dial up a little more, and the primarch all but squirmed with pleasure—then turned it off again, just as quickly. Sandalphon couldn’t hide his frustration, letting out another expectant whine.

“Djeeta…” he said. “Please…!”

“You want more?”

_“Yes!!”_

“Then say so.”

Djeeta didn’t want to admit it, but she was having way, _way_ too much fun toying with him like this. Moving the goalposts, little by little, and watching him helplessly try to keep up… of course, she wouldn’t keep him hanging for too long; eventually she’d reward his patience. She’d set the dial as high as it would go and and watch him lose himself in pleasure.

Sandalphon looked back at her, finally; the pure _lust_ in his eyes made her heart skip a beat.

“More…” he said—_Astrals_, he sounded so pitiful like this; Djeeta almost had to laugh. “Please… Please turn it back on…!”

“How can I say no, when you ask so sweetly?” Djeeta responded. She finally gave him what he wanted, turning the dial up to the halfway point. Sandalphon practically dissolved, a pathetic moan escaping his throat as his body reeled with sensation. His back arched, his hands grappled for purchase in the sheets—he needed something to hold on to, anything to keep him grounded while the vibrator threatened to completely undo him. Djeeta was getting hot and bothered just watching him succumb to it, knowing that he was at her mercy.

“Heheh, this is great,” Djeeta said with a meaning smile. “It seems I’ve found a new hobby in sadism…”

Sandalphon nearly choked; he tried to glare at her over his shoulder, but his face was so flushed and frantic that it didn’t have nearly the intended effect.

“_Really!?_ _Right_ now!?”

“Sorry, couldn’t resist poking a little fun,” Djeeta admitted. “You really are too easy sometimes, Sandalphon.”

Thinking to reward him for putting up with her, Djeeta turned up the dial. Sandalphon let out a startled yelp.

“Ooh, this _is_ fun.”

_“Djeeta—!”_

“It’s fun seeing you like this,” Djeeta went on, languidly twirling the controller by the cord. “I don’t usually get to see you so… _desperate._ You really want it, don’t you?”

“Yes… I… I really do… ” Sandalphon murmured into the pillow, the words coming out slurred. Djeeta could tell he was nearing his limit. She’d seen him like this a few times before: worked up to the point of dizziness, eyes barely registering anything in front of him, words slurring on his lips. He was practically drunk with lust—and Djeeta knew he still had a bit more left in him.

“I can’t hear you, angel,” she teased. “Do you want more?”

Sandalphon lifted his head, mouth hanging open as the words fell from his lips:

“Yes…! More, _please…!”_

“You want me to make you come?”

“I’ll do anything…! Just, please…!” Sandalphon whined in frustration, his voice straining with desire, “I’m so close…!”

“Anything?” Djeeta probed.

_“Anything!!”_

“Will you show me your wings…?”

Her question seemed to puzzle him. He looked back at her, brows furrowed.

“My…? That’s all?”

Quickly seeming to realize that questioning her intent wouldn’t be in his favor, Sandalphon added, “Which ones?”

“The brown ones,” said Djeeta. “I did say _your_ wings, didn’t I?”

“Heh,” he conceded, weakly, “You did, yes.”

There came a soft glow, and a pair of brown wings appeared at his back just above the waist. Even folded, they took up considerable space on the bed. Djeeta admired them for a while, watching him clumsily find the most comfortable place to set them down. Before long, though, she realized she couldn’t be satisfied just looking anymore; she leaned forward and laid a gentle kiss between his wings.

“Ah…!”

Careful of the vibrator cord, Djeeta lay down on top of him, curling her body against his. Sandalphon melted at her touch, his whole body relaxing into her. With her skin against his, she could faintly feel the vibrator still pulsing within him—and his core humming feverishly against her chest in tandem.

“Djeeta…!”

Djeeta answered him with another kiss, this time at the nape of his neck.

“You’re so beautiful, Sandalphon…. You’ve been so patient for me…”

“Ohh…” Sandalphon could only moan in response; he was too far gone to think of anything to say back to her.

“I think you’re more than deserving of a reward,” Djeeta went on, kissing his shoulders softly. “Here…”

Djeeta reached down and around his waist, grasping the primarch’s waiting cock. Sandalphon jumped at her touch and bucked helplessly in her grip, wordlessly begging her to do more than just hold him. Djeeta smiled to herself. With her other hand, she nudged the dial up as high as it would go.

The effect was immediate. Sandalphon’s breath caught in his throat; his core burned hot against her chest. His wings flapped helplessly at his sides, scattering feathers across the bed. For her part, Djeeta held on tightly in the chaos—she hardly had to do anything; the vibrator had already pushed him over the edge, and his own thrusts drove his cock up between her fingers.

“Ohh…!! Djeeta, I’m….!”

As he finally reached his long-awaited climax, Sandalphon’s voice tumbled from his mouth in a sound that was more scream than moan—it was loud enough that Djeeta got the feeling that half the ship had heard it. She didn’t care whether anyone had, of course. Her relationship with Sandalphon was no secret among the crew, and this was hardly the first time they’d made a bit of noise together. Neither was this the first time he’d spilled himself all over her hands and sheets.

For a few moments, there was quiet—aside from the low hum of the still-running vibrator and the primarch’s exhausted panting. Djeeta mercifully switched the vibrator off, and Sandalphon let out a sigh of relief. She shifted to lay down next to him on the bed, careful to move his wing out of the way, and took some time to admire him while he came down from his high. Hair tossed, eyes glazed, legs quivering—even as a post-coital mess, he was so beautiful… Djeeta once again felt lucky that this kind of view was hers alone.

“You alive in there?” Djeeta asked.

“I don’t know…” Sandalphon murmured in response. “I was seeing stars for a minute there. You… you really did a number on me… ”

Djeeta couldn’t help giggling to herself, proudly.

“Glad you had fun.”

Sandalphon looked over at her, smiling lopsidedly—his expression fatigued and sated and full of love, all at once. It made Djeeta’s heart dance to see him looking so relaxed; for him to be looking at her like she was the only thing in the world. Like she was his solace. She wished she could capture this moment forever, and keep it with her for the times when the world got too difficult to handle…

Realizing that the liquid on her hand was starting to dry, Djeeta reached for her nightstand, where she kept a small stack of towels.

“Here, let’s get you cleaned up. I’ll take that vibrator out, too.”

“Thank you…”

Cleanup was quick; a new blanket would be required, but otherwise the mess was fairly contained. Sandalphon jumped a little as Djeeta carefully pulled the vibrator out of his ass.

“I’ll have to remember this one for next time,” she said coyly, wiping it off with a towel. “Seems like it was a big hit.”

“Yes, absolutely,” Sandalphon agreed. “I was a bit nervous about using tools to augment sexual play at first, but…” He paused, a smirk on his lips. “Well, let’s just say that skydweller ingenuity continues to impress me.”

“And your core’s alright?” Djeeta asked. “It got pretty hot back there, so I got a little worried…”

“It’s fine. More than fine.” Sandalphon brought a hand to his chest. “It, ah… when it reached resonant frequency, the effect was… akin to orgasm.”

“Huh. Good to know.” Djeeta would _definitely_ be filing that information away for later. “I’m glad you liked it so much, Sandalphon. I had a good time watching you.”

“Hm? You were satisfied just watching?” Sandalphon rested his head on his hand invitingly, using the other to run a meaning trail up her thigh with his fingers. “Somehow, I don’t think that’s true.”

“Yeah… you got me…” Djeeta admitted. He really did know her better than anyone, at this point. “I’m, uh… I’m pretty worked up, still…”

The sound of his desperate, wanting voice had been burned into her memory; she would probably get all hot and bothered just thinking about it for weeks.

“Heh. You’re so easy to read,” Sandalphon teased. His fingers brushed over her waist. “I don’t suppose you’d like to blow off a little steam?”

“If you’re up for it…” Djeeta looked away, flushing. “You seemed pretty spent, so…”

“Nonsense,” Sandalphon answered. He traced a delicate line down to the blond curls between her legs. “I always repay my debts.”

“Heh, alright then,” said Djeeta coyly, scooting closer to him. She reached up to hold his face in her hands, pressing her lips to his for a brief, stolen kiss. “Make me come, Sandalphon. I want the whole ship to know.”

**Author's Note:**

> djeeta using sandalphon's own edgelord lines against him is a running theme in my fics (and in canon tbh)
> 
> if the ending seems kinda rushed: it was lmao i just kinda wanted to get this idea out the door, finished is better than perfect, etc
> 
> anyway if u got this far thank u for reading!!!! and if u liked this one i have many more sandjeeta fics where this came from >:3


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